I also updated meas_base, meas_algorithms and meas_astrom (all of which needed small changes due to missing includes) to use geom and did some C++ cleanup (clang-format and modernizing some old namespace usage).

I've attached depr.cc as an example of how we could use the [[deprecated] tag on the backwards-compatibility typedefs. As discussed on the afw PR, I think adding those would be a bit problematic, but maybe we can find a creative way to get the upside of that without the downsides.

Review complete.  There are a few minor comments on the PRs, with the only big open question being Krzysztof Findeisen's deprecation idea.  As noted on the PRs, I did not look carefully at obvious find-replace commits; please let me know if I should in any particular cases.

Thank you for the helpful review. geom updated as per request.